Tarhana, a fermented wheat flour-yoghurt mixture used in soup making, was produced in ready-to-eat form using canning. The effects of rotation speed (6.6-8.4 rpm), dry solids content (33.0-41.9% w/w) and retort time (3.20-3.80 min) on the starch gelatinization and protein in vitro digestibility (PIVD) of the samples were analysed using response surface methodology. Increasing rotation speed and retort time resulted in increased starch gelatinization (p > 0.005). Rotation speed had more effect on starch gelatinization than retort time. Changes in dry solids content of the soup did not have any significant (p > 0.005) effect on starch gelatinization. The PIVD values of the samples did not change significantly (p > 0.05) in all canning conditions studied. (C) 2003 Elsevier Ltd. All rights reserved.